The present invention relates to an oil and fat composition used for frying, and more particularly it relates to a frying oil and fat composition which shows good fluidity at room temperature, is not or is hardly solidified (or crystallized or coagulated) at room temperature, and also suffers little deterioration of its quality after heating in use.
Vegetable oils are oils derived from vegetables. Liquid state one such as rapeseed oil, and solid or half-solid state one such as palm oil and coconut oil are both called vegetable oil. Therefore, in the present invention, the vegetable oil which is solid or half-solid at room temperature is distinguished from the one which is liquid at room temperature, and is hereinafter described as vegetable "fat". These vegetable oils and fats are used for applications where they are used to make the most of their respective properties--liquid, or solid or half-solid at room temperature.
Vegetable fats such as palm olein oil and hardened soybean oil are favorably used for frying doughnuts, croquettes and the like as they can create a more palatable crispness and a lighter texture than when using vegetable oils such as corn salad oil and rapeseed oil. These vegetable fats have good heat stability and can stay in a semisolid state at around room temperature (20-25.degree. C.), so that they are popularly used for frying various kinds of fryer stuff. Also, inexpensiveness of these vegetable fats contributes to reducing the cost of the blended oil and fat preparations by increasing the mixing percentage of the vegetable fats. However, these vegetable fats or the blends with other oils and fats have the problem that they are inconvenient to use because of lack of fluidity and their tendency to solidify in the practical temperature range from 0.degree. C. to room temperature. It has been pointed out that when the temperature of the storage environment of these vegetable fats is low, for instance in winter, their fluidity lowers to make it hard to take out from the container. Thus, techniques for preventing solidification of these oils and fats in the temperature range of around 0.degree. C. to 20.degree. C. and maintaining enough fluidity in such temperature range despite of formation of small quantities of solid fat crystals, have been demanded.
When the vegetable fats such as palm olein oil and hardened soybean oil are left in the air and allowed to cool by itself after used for frying, they are solidified as the ambient temperature drops, so that a considerable time is required for heating when resuming the frying operation the next day. Since such solidification of oils and fats is accelerated as their heat history prolongs, those oils and fats which are not or hardly solidified at around room temperature, have been demanded.
Further, the oils and fats for frying are subject to progressive deterioration of their quality in heating to cause a rise of carbonyl value or peroxide value, so that usually an anti-oxidizing agent such as tocopherol is added for preventing these phenomena, but its effect is unsatisfactory.
For preventing the vegetable fats from solidifying or for retarding their solidification at low temperatures, there have been known, for instance, the methods in which (1) a low-melting point vegetable oil containing an unsaturated fatty acid such as oleic acid in abundance is added, and (2) a sucrose lauric acid ester.
These methods, however, involve undesirable problems. In use of the vegetable oils and fats for frying, it is required that they contain solid fat (microcrystallized fat) for giving a savory effect, but if the content of such solid fat is high, it becomes not only difficult to control separating of solid fat or to retard solidification at low temperatures by the said conventional methods (1) and (2), but there also remains a smell of laurin in the fries to spoil their relish.
Various techniques, for example, a cold-resistant vegetable oil composition comprising of cold-resistant vegetable oil, polyglycerin fatty acid ester, sucrose fatty acid ester and lecithin, in Japanese Patent Application Laid-Open (KOKAI) No. 5-209187 have been proposed for overcoming this problem of solidification of frying oils and fats at low temperatures, but this proposal has not satisfied to solve the above-mentioned problems.